The present invention relates to mounting arrangements for a transverse mounted engine. The present invention in particular relates to front wheel drive automotive vehicles with transverse mounted engines.
In the most recent quarter century there has been an effort to increase fuel economy of automotive vehicles. Several technical trends have developed to achieve increased fuel economy. One such technical trend is front wheel drive. In a front wheel drive vehicle the weight of the engine is placed over the tractive wheels of the vehicle. The increase in traction due to the engine weight on the tractive wheels, provides an increase in fuel economy.
In front-wheel-drive vehicles, it is a typical practice to have the engine and transmission mounts cushion the torque reaction of the differential as well as that of the engine and transmission. As used hereinafter, the terms xe2x80x9cmountedxe2x80x9d and xe2x80x9cmountingxe2x80x9d refer to the mounting of the unit of the engine block transmission housing and transaxle. Where the engine and transmission are mounted longitudinally in the vehicle, the torque reaction of the differential is in the pitch direction relative to the vehicle while the torque reaction of both the engine and transmission is in the vehicle roll direction. As a result, the torque reaction of the differential is not difficult to deal with at the cushion mounts for the engine and transmission since the pitch forces on the powertrain may be simply resisted by their vertical spring rates while adequate roll resistance is retained for the engine and transmission. However, in the case where the engine and transmission are mounted transversely in the vehicle, their torque reaction is then in the pitch direction and the torque reaction of the differential which is also in the pitch direction is then directly coupled therewith. This imposes a much greater duty on the cushion mounts supporting the engine and transmission since the pitching forces in addition to the normal engine and transmission torque reaction are then influenced by the product of the axle ratio at the differential and the acting transmission ratio.
Irrespective of the relative position of the engine and transmission in the vehicle, it is desired that the cushion mounts be located adjacent the points of minimum vibratory force in the system, i.e. the node points, to derive maximum benefit in isolating the vibration of the sprung mass including the differential. However, typically there is little space for a conventional cushion mounting arrangement capable of effectively controlling and isolating pronounced powertrain vibrations and particularly the pitching (engine roll) motion thereof where both the engine and transmission are positioned transversely in the vehicle.
Another factor which significantly affects the vibration of a mounted engine in a transverse mounted engine vehicle is shift bobble. Shift bobble is caused by the shift characteristics of a transmission. Shift bobble can cause the engine to have a roll motion vibration or a fore and aft movement in the vehicle chassis. This shift bobble will typically be in the neighborhood of 9 hertz plus-or-minus 2 or 3 hertz. The shift bobble is typically perceived as undesirable, particularly when the engine is mounted in a luxury vehicle. The shift bobble is dependent on both the transmission shift strategy and the engine mounting system vibration dynamics. Shift bobble tends to occur most often in the shift between first and second gears.
Stiff engine mounts (also known as cushion mounts) have been shown to provide excellent shift bobble characteristics, while very soft engine mounts create excessive bobble events. The engine mounts also influence many other vehicle characteristics, so that the choice of the spring and dampening rates of the engine mounts cannot be dictated by shift bobble events alone. The requirements for good shift events appear to be at odds with the requirements for good engine vibration isolation wherein less stiff engine mounts are desired. Fortunately, the above is not the actual case. Good shift bobble characteristics of the engine mounts require that the engine roll rate (stiffness) be high, while the engine bounce rate stiffness (up and down motion) should be low for good vibrational isolation. Current practices of increasing the engine roll rate without affecting the bounce rate is with the addition of a roll restrictor. Roll restrictors are also commonly referred to as torque struts. Torque struts usually attach to the vehicle body adjacent the shock tower or the engine compartment fire wall and therefore add a significant path for engine generated sound to enter the vehicle passenger compartment which is on the opposite side of the fire wall.
It is desirable to provide an engine mounting system for a transverse engine mounted vehicle which minimizes engine roll while having minimal affect or no affect upon the engine bounce rate. It is still another desire of the present invention to provide a mounting arrangement which is resistive of engine roll, is inexpensive and does not require extensive modification of present engine, frame or engine mount designs.
To make manifest the above-delineated desires, the disclosure of the present invention is brought forth. In a preferred embodiment, the present invention reveals an engine mounting arrangement for a front wheel drive vehicle with a transverse mounted engine. The mounting arrangement includes a vehicle frame which supports the engine and the engine compartment. The engine is supported on engine mounts similar or identical to those known in the art. A U-shaped torsion bar having extending lever arms is bracketed to the top of the engine block. The torsion bar and its integral lever arms are formed from a tubular member. Vertical extensions extend vertically down from the end of the lever arms and are fixedly connected with the supporting frame underneath. The torsion bar acts as an anti-roll bar for the engine and resists roll motion of the engine in both the fore and aft vehicle directions. However, the suspension bounce rate is left unaffected. The torsion bar and lever arm combination of the present invention does not require any connection to the fire wall or shock tower of the vehicle. Accordingly, there is no transfer via a torque strut of engine vibration to the passenger compartment. The torsion bar lever arm combination of the present invention significantly reduces engine roll events due to shift bobble. Accordingly, the driver of the vehicle perceives a higher quality driving experience.